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Uranium isotopic compositions, 234 U / 238 U activity , are utilized by earth surface disciplines as chronometers and source tracers, including in soil science where aeolian dust is a significant source to the total nutrient pool. However, the 234 U / 238 U activity composition of dust is under characterized due to material and analytical constraints. Here we present new uranium isotope data measured by high precision MC-ICP-MS on ten airborne dust samples collected on the M55 trans-Atlantic cruise in 2002. Two pairs of samples are presented with different size fractions, coarse (1–30 μm) and fine ( 234 U / 238 U activity of mineral aerosols transported from the Sahara across the Atlantic. Our results indicate 234 U / 238 U activity above one for both the water soluble (1.13–1.17) and the residual solid (1.06–1.18) fractions of the dust; no significant correlation is found between isotopic composition and travel distance. Residual solids indicate a slight dependance of 234 U / 238 U activity on particle size. Future modeling work that incorporates dust isotopic compositions into mixing or isotopic fractionation models will need to account for the wide variability in dust 234 U / 238 U activity .